Magnetic field sensors may be used for detecting and measuring a movement or position in a variety of applications. Generally, in such settings, a magnet arrangement is moveable relative to one or more magnetic field sensors. By this relative movements, the magnetic field sensors experience a varying magnetic field and thus may detect the movement.
A particular application is the measurement of rotational speeds, for example in automotive applications. In such applications, usually a pole wheel (i.e., a wheel, disc or circle where magnets are arranged with alternating poles on a circumference) or a tooth wheel (a toothed magnet) is arranged coupled to a rotational axis, such that a magnetic field sensor, which is stationary relative to this axis, experiences a varying magnetic field when the wheel rotates due to the rotation of the axis. In case of a constant rotational speed, the modulation of the magnetic field in such settings often is periodic.
Such sensors are for examples used in anti-lock braking system (ABS) sensors to measure the revolution speed of each tire of a car. In such an application, for example pole wheels having 48 pole pairs are used. Typical conventional sensors then capture the varying magnetic field caused by rotation of the pole wheel and generate a pulse for example at each zero crossing of the sensed field or a signal derived therefrom, resulting in 96 pulses per revolution of the tire in this example. For a typical tire circumference of 2 m this means a spatial resolution of 2 cm.
However, for some applications such a resolution may be insufficient. For example, for car parking systems where a car parks autonomously, the car often moves very slowly. With a resolution of 2 cm, this may cause a comparatively long time between the above mentioned pulses, such that the position of the car based on such sensors may not be updated often enough to enable precise parking. Therefore, a higher resolution of such sensors would be desirable for some application.
One straightforward way to increase the resolution would be to increase the number of pole pairs in the pole wheel (or the number of teeth in a toothed magnetic wheel). However, this increases manufacturing costs for the pole wheel or tooth wheel, in particular if for example a doubling of the resolution is needed.